The following report highlights a near miss with H2S.
A tank inspection was being carried out on board a tanker on completion of discharge. The inspection involved the Chief Officer, cargo inspector and an AB – they were checking tanks with a portable (closed type) gauging tape, which is achieved through a vapour lock arrangement.
At 5P COT the AB opened the vapour lock valve without checking if the cap was securely screwed on or manually holding the cap in place. The inert gas pressure inside the tank (about 500 mm/wg) ejected the cap and detached it from the safety chain to a height of about 50cm, nearly hitting the AB in the face and releasing cargo vapours on deck with H2S content of 700ppm. Fortunately, nobody was injured.
The members of the MAB noted the following points:
- the dangers of H2S are well known. Equally H2S and carelessness are not a good combination
- this simple act of carelessness very nearly resulted in an injury and could easily have proved fatal. One breath in and a person could be unconscious with that level of H2S.
- a surveyor was killed some time ago carrying out a similar operation when he took one breath of air contaminated with 2000ppm H2S.
- it was considered that 500 mm/wg was an excessive IG pressure to be undertaking post discharge tank inspections. Allowing the IG pressure to reduce towards the end of the cargo operation would have reduced the hazard of this incident and reduced the potential for pollution.
- there were three people involved in the tank inspections. If they had worked as a team there could have been better monitoring, and if they were dealing with two tanks at once then adding an extra person would have aided oversight and probably have prevented this incident.